When purchasing an off$-$the$-$shelf application, to which phase of the SDLC is the postimplementation support and service equivalent?

Some organizations charge the purchase price of an application that serves only a particular organizational unit back to the unit. Why does the existence of a charge$-$back arrangement create an incentive to have users develop their own applications?

Why don't users commonly document the applications they develop? Why is poor documentation a problem?